Agricultural balers typically comprise two main parts used in the formation of the bales, being a pre-compression chamber and a baling chamber. Crop material is gathered and pushed into the pre-compression chamber, where a slice of crop material is formed. Pre-compression chamber is linked to the baling chamber in such a manner that the slice of crop material can periodically be transferred into the baling chamber. In the baling chamber, a plunger reciprocally moves, thereby pressing a square bale from subsequently feeded slices.
The plunger movement is powered via a main shaft driven by a motor. Thereby, the motor can be a part of the baler, or can be a part of the puller (tractor) connected to the baler via a power take-off (PTO).
The pre-compression chamber is adapted for receiving gathered crop material. To this end, the pre-compression chamber shows an inlet. The pre-compression chamber furthermore shows an outlet towards the baling chamber. Between the inlet and the outlet, a channel is defined in which crop material can gather into a slice of crop material. The pre-compression chamber comprises a slice pushing mechanism provided for pushing a slice of crop material formed in the pre-compression chamber through the outlet of the pre-compression chamber into the baling chamber. Thereby the slice of crop material is pushed in the baling chamber, after which the plunger can propel the crop material into the baling chamber, thereby pushing the most recently entered slice into the baling chamber, making it a part of the square bale.
The pre-compression chamber comprises, for the purpose of pushing the slice into the baling chamber, a slice pushing mechanism. Different types of slice pushing mechanisms are known, among which fingers grasping behind the slice and pushing the slice through the outlet, or a set of conveyer belts in between which the slice is formed, and which conveyer belts are driven to push the slice through the outlet.
Synchronization of plunger movement and slice pushing movement is typically realized by mechanically linking the plunger driving mechanism and the slice pushing driving mechanism. Such mechanical link ensures proper synchronization, as the slice pushing mechanism is mechanically driven by the plunger movement, it cannot move out of synchronization.
A drawback of the known agricultural balers is that mechanisms to determine the length of the bales are complex and unreliable.
U.S. Pat. No. 5,783,816 shows a bale measuring apparatus using measuring wheels for measuring the strings used by the baler to wrap the bale. The measuring wheel includes a plurality of teeth and is used with an optical beam generator and optical beam detector. The string is wrapped around the wheel and turns the wheel when it is pulled by the moving bale. The device of U.S. Pat. No. 6,708,478 regulates the bale length by using sensors which detect the forward and backward movement of a measuring wheel by the crop material inside the baling chamber. Also, AU 2010101429 discloses the use of e.g. an optical sensor attached to a circular disc or wheel which contacts the bale.
The disadvantage of these solutions is that an indirect measurement is used to determine the actual movement of the bale. Since balers operate on extreme conditions (high and cold temperatures, high pressures, . . . ), indirect measurements may be inaccurate and unreliable.
To this end the invention provided in an agricultural baler comprising a baling chamber and a pre-compression chamber, wherein the pre-compression chamber is adapted to gather crop material and to periodically form a slice of said crop material and push the slice towards the baling chamber into a first segment of the baling chamber, the baling chamber comprising a plunger provided for reciprocally moving in the baling chamber thereby compressing slices of crop material into a bale, wherein at least one optical bale length sensor is provided directly adjacent the crop material in the baling chamber for measuring the length of the passing-by bale by detecting the surface of the crop material in the baling chamber.